Various masks, coverings, garments and shelters are known for providing protection against contaminants, such as hazardous chemical and biological agents. Gas masks provide some protection by filtration means, however, the benefits of a mask are limited, among other things, by difficulty in obtaining proper fit and lack of skin protection. Chemically resistant materials are known for use in protective garments and the like to provide protection from direct skin contact. For example, air permeable protective garments made of adsorbent filter material affixed to air permeable textile supports are disclosed in U.S. Pat. Nos. 4,510,193, and 4,153,745. Materials permeable to both water vapor and air advantageously provide enhanced wearer comfort, and such garments may be used in combination with gas masks to achieve both respiratory and skin protection. Disadvantageously, adsorbent filter layers used in garments are often heavy and bulky while not providing complete protection, and gas mask filter cartridges have limited life requiring replacement when filtration capacity has been expended.
Numerous fluid impermeable casualty bag and shelter designs have been developed in an effort to maintain separation between safe and hazardous environments. Certain impermeable shelters may provide overall protection against liquid and gaseous challenges to one or more persons. However, such systems are also heavy and bulky, and rely on detoxified air from external air supply systems which require a power source. For example, U.S. Pub. No. 2004/0074529 teaches a self-contained and ventilated temporary shelter that includes first and second temporary living spaces made of a hermetically sealed casing, and an air purification system. The air purification system provides a source of filtered air to the shelter, and includes a filtration media to filter out chemical agents, a hepa filter for microscopic organisms, and a UV germicidal filtration unit to filter out pathogens. The air filtration system is powered by AC/DC or an alternate power source.
WO 2004/037349 teaches a protective bag for enclosing at least one human body, made of a multilayered plastic impermeable to hazardous chemicals. To improve the impermeable nature of the bag, an air compressor unit or other means for maintaining a positive air pressure within the bag is optionally included, and a pressure-activated one way valve is adapted to permit excess air pressure to exit the bag. An external air source, such as an oxygen tank or mechanized air filter capable of extracting purified air from a contaminated environment and injecting it into the bag, may be used. A gas mask protects against inhalation of lethal gases, and enables easier breathing through non-mechanized filters by increasing suction forces on the filters. As noted above, filters have limited life and must be replaced when filtration capacity has been expended.
For increased protection and to extend useful life of protective filters, excess adsorbent, such as activated charcoal is often added to the system creating additional weight and bulk. Methods of extending the life of the filter to avoid the expense and the logistical burden of replacement have been sought to solve this problem. U.S. Pat. No. 5,082,471 teaches a life support system for personnel shelter in which the levels of toxic agent to which the filter unit is exposed is reduced, thus extending filter life. The system comprises a shelter and equipment for sustaining a breathable atmosphere within the shelter. A supply of fresh air is fed to a membrane separation unit that is highly selective to the permeation of oxygen over toxic agents, producing an oxygen enriched permeate stream that passes through a unit containing a sorbent to remove remaining traces of toxic material before being fed into the shelter. Carbon dioxide is removed by either maintaining a high air flow into and out of the shelter, or by withdrawing air from the shelter, treating it in a separate unit of equipment, and returning the treated air to the shelter. The additional equipment required to provide air and remove carbon dioxide results in a system that is particularly heavy, large and bulky.
Disadvantageously, known enclosure systems which maintain a source of airflow, are often heavy and bulky due to the need for high filter agent adsorbent loadings. Moreover, enclosure systems that rely on external airflow systems to achieve levels of oxygen necessary to sustain life disadvantageously require a power source. What is desired is an air permeable protective enclosure system that provides high levels of protection against hazardous gaseous, vapor, or aerosol chemical and biological agents, without the need for heavy, bulky filtration units using minimum sorbent to reduce weight and increase flexibility. Moreover, it would be desirable for this protective enclosure system to be simultaneously capable of providing life-sustaining levels of oxygen within the system without relying on supplemental air supply sources.